1. Field of the Invention
The present invention relates to a method for transmitting an uplink signal including control information and data through an uplink channel.
2. Discussion of the Related Art
Channel Structure and Mapping of LTE
The link channel structure and mapping of the 3rd generation partnership project (3GPP) long term evolution (LTE) will now be described. A downlink physical channel includes a physical downlink shared channel (PDSCH), a physical broadcast channel (PBCH), a physical multicast channel (PMCH), a physical control format indicator channel (PCFICH), a physical downlink control channel (PDCCH), and a physical hybrid ARQ indicator channel (PHICH). An uplink physical channel includes a physical uplink shared channel (PUSCH), a physical uplink control channel (PUCCH), and a physical random access channel (PRACH).
A downlink transport channel includes a broadcast channel (BCH), a downlink shared channel (DL-SCH), a paging channel (PCH), and a multicast channel (MCH). An uplink transport channel includes an uplink shared channel (UL-SCH) and a random access channel (RACH).
FIG. 1 illustrates a mapping relationship between a downlink physical channel and a downlink transport channel. FIG. 2 illustrates a mapping relationship between an uplink physical channel and an uplink transport channel. The above-described physical channels and transport channels are mapped to each other as illustrated in FIGS. 1 and 2.
Meanwhile, a logical channel classified as a control channel includes a broadcast control channel (BCCH), a paging control channel (PCCH), a common control channel (CCCH), a multicast control channel (MCCH), and a dedicated control channel (DCCH). A logical channel classified as a traffic channel includes a dedicated traffic channel (DTCH) and a multicast traffic channel (MTCH).
FIG. 3 illustrates a mapping relationship between a downlink transport channel and a downlink logical channel. FIG. 4 illustrates a mapping relationship between an uplink transport channel and an uplink logical channel.
Slot Structure of LTE
In a cellular orthogonal frequency division multiplexing (OFDM) radio packet communication system, an uplink/downlink data packet is transmitted in units of subframes. One subframe is defined as a prescribed time duration including a plurality of OFDM symbols.
The 3GPP supports radio frame structure type 1 applicable to frequency division duplex (FDD) and radio frame structure type 2 applicable to time division duplex (TDD).
FIG. 5 illustrates the radio frame structure type 1. The radio frame type 1 consists of 10 subframes. One subframe consists of 2 slots.
FIG. 6 illustrates the radio frame structure type 2. The radio frame type 2 is comprised of two half-frames. Each half-frame consists of 5 subframes, a downlink pilot time slot (DwPTS), a guard period (GP), and an uplink pilot time slot (UpPTS). One subframe consists of two slots. The DwPTS is used for an initial cell search, for synchronization or for channel estimation. The UpPTS is used for channel estimation in an evolved Node B (eNB), uplink transmission synchronization of a User Equipment (UE). The GP is an interval for eliminating interference caused by multi-path delay of downlink signal between uplink and downlink. Namely, irrespective of a radio frame type, one subframe consists of two slots.
FIG. 7 illustrates a downlink slot structure of LTE. As illustrated in FIG. 7, a signal transmitted in each slot may be represented by a resource grid comprised of NRBDLNSCRB subcarriers and NsymbDL OFDM symbols. At this time, NRBDL denotes the number of resource blocks (RBs) in a downlink, NSCRB denotes the number of subcarriers constituting one RB, and NsymbDL denotes the number of OFDM symbols in one downlink slot.
FIG. 8 illustrates an uplink slot structure of LTE. As illustrated in FIG. 8, a signal transmitted in each slot may be represented by a resource grid comprised of NRBULNSCRB subcarriers and NsymbUL OFDM symbols. At this time, NRBUL denotes the number of resource blocks (RBs) in an uplink, NSCRB denotes the number of subcarriers constituting one RB, and NsymbUL denotes the number of OFDM symbols in one uplink slot. A resource element refers to one subcarrier and one OFDM symbol as a resource unit defined by indexes (a, b) (where a is an index on a frequency domain and b is an index on a time domain) within the uplink slot and the downlink slot.
Meanwhile, the eNB transmits control information to a downlink to control a UL-SCH which is an uplink transport channel. The control information transmitted to the downlink informs the UE of the number of RBs transmitted through the UL-SCH and a modulation order. In addition, when data is transmitted to an uplink, the control information informs the UE of a payload size of the data. The payload size may be defined as the sum of the size of information (e.g., the size of data, or the size of control information) transmitted from a medium access control (MAC) layer and the size of cyclic redundancy check (CRC) attached arbitrarily to the information in a physical layer. The payload of the control information may not include the size of the CRC because the CRC cannot be attached to the control information according to the size of the control information before the CRC is attached to the control information. Specifically, if the size of the control information to which the CRC is not attached is smaller than or equal to 11 bits, the CRC is not attached to the control information. In addition, if the size of the control information to which the CRC is not attached is greater than or equal to 12 bits, the CRC is attached to the control information.
Data and control information (e.g., Channel Quality Information (CQI)/Precoding Matrix Indicator (PMI) or Rank Indication (RI)) may be multiplexed together and transmitted through the UL-SCH. In the conventional system, a scheme for encoding the data differs from a scheme for encoding the control information. Furthermore, in the conventional system, a block error rate (BLER) of the data and a BLER of the control information, demanded by the eNB, may differ from each other.
Furthermore, in the conventional system, even though a code rate of data is known using the modulation order, the number of RBs, and the payload size of data, a code rate of control information cannot be known. Moreover, since the data and the control information are multiplexed together and then transmitted through the UL-SCH, the number of transmitted symbols of the data cannot be known.
To solve such problems, the conventional system was upgraded such that the code rate of the control information is compensated for by an offset that can be changed by the eNB as compared with the code rate of the data.
Even if the system is managed as described above, the code rate of the data may be varied by information multiplexed with the data. Moreover, if the data is not transmitted, the UE cannot estimate a code rate of CQI/PMI or rank indication for example. Accordingly, a method for calculating a code rate of transmitted information (e.g., CQI/PMI or rank indication) according to a combination of information transmitted through the UL-SCH is demanded.
Also, in the conventional communication system, if an error occurs in a data packet due to failure of receipt after the data packet is transmitted, the corresponding data packet is re-transmitted.
Also, in the case where re-transmission occurs, if decoding is performed using an initially received data packet and a data packet received by re-transmission, a success probability of receiving the data packet is increased even though not all resources employed when the data packet is initially transmitted are used.
For example, when the communication system operates such that the initial data packet is transmitted without errors with a probability of 90%, the system does not encounter any problem even when the data packet is re-transmitted at a code rate higher than a code rate of the initial data packet. Transmitting a data packet at a high code rate means that less physical transmission resources are used than during the initial transmission of the data packet.
If a code rate of CQI/PMI or rank indication is calculated using the total number of symbols of the data when re-transmitting the data packet, a code rate for stably transmitting the CQI/PMI or rank indication may not be set. Therefore, when data is re-transmitted, a code rate setting method for stably transmitting the CQI/PMI or rank indication is demanded.
In summary, in an attempt to save bandwidth while retransmitting, a conventional mobile is commanded by a base station to reduce the amount of total information bits (i.e., data and control bits) that are retransmitted. This does not result in an increased error rate for the data bits because the retransmitted payload data is soft combined with the original payload data. However, corresponding control data of the two signals are not combined for decoding/demodulation. That is, in the conventional system, the truncated control bits of the retransmitted signal are used for code rate setting, resulting in degraded performance. Thus, the present invention compensates for this degradation in performance by reusing the original control data in a novel fashion.